Complete HarpWeek Explanation:In this Chicago Rail Splitter cartoon, Northern Democratic presidential nominee Stephen Douglas is portrayed as a carnival conman, a “Thimble Rigger.” He uses sleight-of-hand to fool bettors that they can find an item hidden underneath one of three thimbles, “Popular Sovereignty,” “Dred Scott,” and “Wickliffe.”

“Popular Sovereignty” was an idea promoted by Douglas, which declared that territorial voters, not the federal government, should decide whether or not to legalize slavery. “Dred Scott” was the U.S. Supreme Court decision (1857) declaring that blacks were not citizens and slavery could not be banned from the territories. The ruling made the core of Douglas’s popular sovereignty proposal unconstitutional. However, he responded by arguing that territorial legislatures could refuse to enact laws supporting the institution (called "slave codes"), which would effectively prevent slavery from surviving there.

“Wickliffe” was Governor Robert Wickliffe of Louisiana, a Southern supporter of Douglas. At the rump National Democratic Convention that nominated the Illinois senator for president, Wickliffe authored a platform plank affirming the supremacy of the Supreme Court to determine the constitutionality of territorial acts. It was an attempt to gain Southern backing for Douglas and was believed to be ambiguous enough to retain Northern allegiance. However, to the featured cartoonist and other critics, the Wickliffe resolution reaffirmed the Dred Scott decision and contradicted the popular sovereignty stance on which Douglas was running.

In the cartoon caption, “$25,000” is the presidential salary, while “little joker” is a cut at Democrats who belittled Lincoln as an inappropriate humorist. “John C.” in the poem is John C. Calhoun, the former senator and vice president who ardently promoted the concept of “state sovereignty”—that state authority is superior to that of the federal government.